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Enhancing New Zealand surf clam fisheries

Farrington, Glenn

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Abstract

With world population increasing the need for sustainable food resources grows with it. Therefore growing the seafood industry for both the domestic market as well as exports, in New Zealand is important both as a source of food, but also for economic gain. In New Zealand, there are 436 species of bivalves, including pipis, cockles, mussels, oysters and scallops (Wassilieff, 2014), this study examines one subset species commonly known as surf clams, a species with export potential. While there has been some limited fishing of these species, the main industry player has identified several impediments to growth. These are, a) the quite low Total Allowable Commercial Catch (TACC) which has limited the ability to create a sustainable business and b) high mortality of live clams that are shipped overseas. This study addresses each of these impediments.

First the biomass of commercially caught species was determined along a 26 km stretch of coast in Fishing Management Area 8 (FMA8, Foxton Beach), to ascertain the biomass of the seven commercially caught species of surf clam, with a view to ascertain how appropriate the current catch limits are, with a view to increase this limit to help drive a growing export business. Only four of the seven species were found with a total of 5.7t of surf clams landed in ten days of fishing. One dominant species, Spisula aequilatera (SAE) consisted of 43% of total catch, followed by Dosinia anus (DAN) 21.9%, Mactra murchisoni (MMI) 21.5% and Paphies donacina (PDO) 13.5%. Upon entry into the quota management system, these four species within FMA8 was set at 67t, from the results found in this study, it has seen an increase to 2816t for the same four species.

Secondly was a biomass survey conducted within Fishing Management Area 7 (FMA7, Golden Bay) with the same view of ensuring the current catch limits are set correctly to ensure sustainability of the species. Only one species (Paphies donacina) was found, and in ten explorative tows, only eight of these tows produced any catch. The total combined weight of these tows was 13.62kg. Due to the tough fishing conditions, lack of species and low catch numbers, the decision was made not to conduct any further investigation of this area.

Finally, experiments were undertaken on the oxygen consumption, and mortality tests. These tests were to replicate the transportation of live clams to ascertain the high mortality rates the industry partner was finding, when live product was shipped overseas. The results for the leakage test of the chilly bins, used to export the clams showed that when filled with 100% oxygen, after 30 hours this had leaked to an average of 24.9%, suggesting that the cause for the high mortality is not due to oxygen depletion. Clams of various sizes, when placed into an air tight chamber used varying degrees of available oxygen, however after 30 hours oxygen consumption was less then available confirming the previous test that it is not due to lack of oxygen for the high mortality. The test to replicate transportation conditions was inconclusive; we were unable to replicate the high mortality rate seen by the industry partner. Using the same methods and duration the control test produced 0% mortality rate for the complete 72hr period, test one had a 0% mortality rate for the first 24hrs, then after 48hrs mortality had raised to .36% and after 72hrs it was .72%. Test two had a 0% mortality rate at re-swim after 24hrs it was .34%, then after 48hrs mortality had risen to 1.71% and stayed at this for the remaining time. Further investigation would need to be carried out to find the root cause of the high mortality seen by the industry partner; two such tests could be measuring temperature inside random chilly bins, as well as some shock device to see if they are being roughly treated and dyeing from shock.